I got the "/services/data/v46.0/parameterizedSearch" POST API working for a complex SOSL search I want to perform. I am referring to the Salesforce documentation here: https://developer.salesforce.com/docs/atlas.en-us.api_rest.meta/api_rest/resources_search_parameterized.htm

My requirement is, I wish to find an email address by only searching the email fields and have the request json payload tailored to do so
 

POST /services/data/v46.0/parameterizedSearch
{ 
"q":"mytestemail+test@example.com", 
"fields":["Id", "external_id__c"], 
"in": "EMAIL", 
"sobjects": [{"name":"Account"}] 
}

Per my understanding if I use "in": "PHONE" it should not yield any results but it does.
 

POST /services/data/v46.0/parameterizedSearch 
{ 
"q":"mytestemail+test@example.com", 
"fields":["Id", "external_id__c"], 
"in": "PHONE", 
"sobjects": [{"name":"Account"}] 
}

Please let me know if I am missing something here.